Sharing memory between guests

ABSTRACT

In an approach to sharing memory between a first guest and a second guest both running on a data processing system, one or more computer processors provide a virtual device to a first guest for proxying memory accesses between the first guest and a second guest, where the first guest is associated with the second guest, and where the first guest is running a first operating system and the second guest is running a second operating system. The one or more computer processors send one or more device related functions to the second guest, wherein the virtual device enables sharing memory between the first guest and the second guest.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of data processingsystems, and more particularly to a method, system and computer programproduct for sharing memory between two virtualized systems running on adata processing system.

A virtualized data processing system can provide multiple views on realand emulated resources of that processing system. Such a view can beimplemented as virtual machines or so-called guests. Each guest operatesas a virtual separate data processing system independent of otherguests. The component providing the view of independent data processingsystems is called a hypervisor. The areas of responsibility of thehypervisor include resource management, emulating, if necessary, andisolation between guests.

Occasionally guests encounter a need to collaborate on a task, e.g. oneguest should analyze data for another guest. In general, thiscommunication is handled by copying data between two guests over avirtual network. This allows facilitation of well-known programmingparadigms. With this approach security and isolation of guests still canbe maintained on a high level.

SUMMARY

Embodiments of the present invention disclose a method, a computerprogram product, and a system for sharing memory between a first guestand a second guest both running on a data processing system. The methodmay include one or more computer processors providing a virtual deviceto a first guest for proxying memory accesses between the first guestand a second guest, where the first guest is associated with the secondguest, and where the first guest is running a first operating system andthe second guest is running a second operating system. The one or morecomputer processors send one or more device related functions to thesecond guest, wherein the virtual device enables sharing memory betweenthe first guest and the second guest.

Further, a computer program product for sharing memory between a firstguest and a second guest both running on a data processing system mayinclude program instructions to provide a virtual device to a firstguest for proxying memory accesses between the first guest and a secondguest, where the first guest is associated with the second guest, andwhere the first guest is running a first operating system and the secondguest is running a second operating system. The program instructionssend one or more device related functions to the second guest, whereinthe virtual device enables sharing memory between the first guest andthe second guest.

Further, a data processing system for execution of a data processingprogram is proposed, comprising computer readable program instructionsfor performing a method described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system diagram of an environment in which a method accordingto an embodiment of the invention is implemented;

FIG. 2 is a flowchart of an exemplary process of the method for sharingmemory between a first guest and a second guest according to anembodiment of the invention; and

FIG. 3 is an example embodiment of a data processing system forexecuting the method according to the invention.

DETAILED DESCRIPTION

In the drawings, like elements are referred to with equal referencenumerals. The drawings are merely schematic representations, notintended to portray specific parameters of the invention. Moreover, thedrawings are intended to depict only typical embodiments of theinvention and therefore should not be considered as limiting the scopeof the invention.

The illustrative embodiments described herein provide a method, system,and computer program product for sharing memory between guests. Theillustrative embodiments are sometimes described herein using particulartechnologies only as an example for the clarity of the description. Theillustrative embodiments may be used for sharing memory between a firstguest and a second guest, the first guest running a first operatingsystem and the second guest running a second operating system, where thetwo operating systems could be the same one, but could also be differentoperating systems.

In a virtual system, both an application running on the first guest andan application running on the second guest are hosted by the samehypervisor (i.e. the same physical machine). Due to an embodiment of theinvention, a mechanism is provided to share data between the two guests,allowing the second guest to operate on data of the first guest.

The first guest identifies the data to be made available to the secondapplication and invokes the second application on the second guest. Thedata for this call is mapped into the address space of the secondapplication by the hypervisor for immediate access. While processing,the second application consumes the resources of the second guest (e.g.CPU, memory, I/O) and still accesses the data provided by the firstguest directly. Translation of addresses of the provided data allowsprogramming of second applications using higher level languages.

In recent developments, compute-intensive parts of the applications aremoved to operating systems with low overhead to perform morecost-effective computation. According to the proposed method it ispossible to avoid copy operations to move in-memory data structure fromone operating system to another operating system. Mechanisms like remoteprocedure call (RPC), TCP/IP sockets, or even remote direct memoryaccess (RDMA), which have to perform copy operations, causing latenciesare not needed to be used.

Eliminating this overhead improves the overall performance of anapplication significantly. An encapsulation of functionality is possiblewithout requiring significant changes in an operating system or theapplication. There is no communication overhead when sharing memoryaccording to an embodiment of the invention. The amount of data sharedis performance irrelevant for a call of service functions, because thereare no copy operations needed for sharing memory. Sharing memory may beachieved by a function call from a guest to another guest.

FIG. 1 depicts a system diagram of an environment, in which a methodaccording to an embodiment of the invention is implemented. The systemdiagram shows first guest 10 and second guest 20, depicted in the FIG. 1as their memory regions, where hypervisor 30 is assigned to both firstguest 10 and second guest 20, and thereby associates first guest 10 withsecond guest 20. First guest 10 is running first operating system 12,e.g., a common mainframe operating system, with first application 16,which incorporates application specific data 15. First operating system12 may include a kernel that can discover applications on second guest20. Second guest 20 is running second operating system 22, e.g., Linux®,with second application 26, for example, an application assist cartridge(AAC) as in FIG. 1, but which may represent any analytical algorithm.Second application 26 is running as one application of user space code28 of second guest 20. Hypervisor 30 contains management module 32 forall collaboration specifics. Application management module 32 can managethe interaction between first guest 10 and second guest 20 regarding theusage of service functions and applications, such as AAC. System call 40(SYSCALL) may be used for registering second application 26 with secondoperating system 22.

The proposed method for sharing memory between first guest 10 and secondguest 20 is used for data 15 of first guest 10, to be used and operatedon by second guest 20 without copying data 15 physically to second guest20. Instead second application 26 may operate with data 15 by using afunction call from first guest 10 to second guest 20 requesting someservices of second application 26, e.g., AAC service functions.

According to the proposed method, hypervisor 30 provides virtual device14 with a direct memory access. Then first guest 10 may announce thememory regions containing data 15 to virtual device 14 and start callingdevice specific functions on that data. Next hypervisor 30 may map thepreviously announced memory regions on top of the already availablememory regions of second guest 20 and dispatch device related functionsto second guest 20. In this way, first guest 10 and second guest 20 areenabled to share the memory via virtual device 14, as virtual device 14can proxy memory accesses between first guest 10 and second guest 20.

Virtual device 14 may be configured with Peripheral ComponentInterconnect (PCI) device semantics. Thus memory regions may beannounced to be used. Registers to pass data exist, for computationalpurposes, as well as for pointers to memory regions. Interruptmechanisms may be used for completion and failures in operation.

Thus it is possible to use the services of second application 26 in theway of a commonly used external board with the functionality of secondapplication 26 to be used by first application 16, where secondapplication 26 may operate on data 15 of first application 16 and modifydata 15. In this way the functionality of the code of second application26 is offered to data 15 of first application 16.

When the service functions of second application 26 are working withmemory regions, the code of the service functions may containdefinitions when memory regions are accessed. Compiler/special datastructures may translate addresses in memory region accesses. The codefurther realizes pointer arithmetics within the memory region. Secondguest 20 gets a base offset for the memory region passed by first guest10.

A base address register of virtual device 14 may be adapted to translatepointers of first guest 10 to pointer locations in second guest 20 inorder to use correct memory data. This may be implemented by, forexample, a C++ encapsulation of the data type, or a change of compilerpointer arithmetics of memory region based data.

Access to second guest 20 may be controlled by a request queue ofscheduler 24 in second operating system 22. This may be useful if anumber of guests are operating on a data processing system with a numberof services being announced. Scheduler 24 may be operating as part of akernel of second operating system 22.

Mapping of the memory of first guest 10 may be implemented as aread-only mapping, such that second guest 20 may only read data 15, andonly first guest 10 is allowed to write on data 15. This may becomeimportant for safety relevant systems. The write protection of thememory area of second guest 20 may be requested by first guest 10 andenforced by hypervisor 30.

Hypervisor 30 may provide information on statistical use of functions ofsecond guest 20. This is enabled by the managing function of hypervisor30 gathering usage information from all services and guests involved inusing data and services. This information may be used for billingpurposes, monitoring, tracing for debugging, logging, and the like.

FIG. 2 depicts a flowchart of an exemplary process of the method forsharing memory between first guest 10 and second guest 20 according toan embodiment of the invention. Data 15 may be shared between firstapplication 16 running on first guest 10 and second application 26running on second guest 20, comprising the steps explained in FIG. 2.

First in step S200, second application 26 running on second guest 20 isregistered with second operating system 22 in order to provide servicefunctions, which may be called by other entities. Second application 26,e.g., AAC, of second guest 20 announces the service functions, alongwith an identification token through a system call. A kernel of secondoperating system 22 then knows that the service functions are served bysecond application 26. Second application 26 announces its readiness toserve a service function through a blocking system call 40: the code ofsecond application 26 will not be executed any further but hangs untilthe kernel schedules second application 26 again (triggered by anexternal event), returning from system call 40. Any schedulingcharacteristics for this service function, e.g., which processors to runon or what priority to use, are derived from the attributes of secondapplication 26. If several instances of a service function are to beserviced in parallel, several threads may issue the blocking system call40. If different services of the service function are to be offered,several processes may run this logic on per AAC base.

Next in step S202, second operating system 22 announces availability ofthe service functions to hypervisor 30. A special paravirtualizedinterrupt is injected into second guest 20 by hypervisor 30 on behalf ofanother consumer of that service, as soon as the consumer requestsexecution of that service function. In one embodiment, second operatingsystem 22 registers an interrupt handler with hypervisor 30 for servicefunctions, such as AAC requests. The kernel of second operating system22 uses a hypervisor call, e.g., a paravirtualized instruction, toannounce availability. The kernel revokes the service functionannouncement from hypervisor 30 as soon as second application 26denounces the service function, or when second application 26terminates.

In step S204, hypervisor 30 announces the service functions to firstguest 10. Hypervisor 30 accepts the service function registration fromsecond operating system 22 and offers the AAC to some or all otherguests. Other guests can probe, or transmit queries, for active servicefunctions and consume them. Policies, isolation/multi-tenancy, backlog,priorities, and access restrictions can apply. A standard servicelocation protocol may be used to implement the registry and discoverymechanism.

Next in step S206, first application 16 running on first guest 10determines the service functions are available by discovering theannouncement by hypervisor 30. Service location mechanisms may be usedas provided by step S204. If first guest 10 intends to use a servicefunction, then first guest 10 may ask hypervisor 30 to make the servicefunction available. If first operating system 12 of first guest 10discovered the service function first, then first operating system 12can enable discovery to its applications. Hypervisor 30 makes theservice function as virtual (PCI) device 14 available, e.g., viahot-plugging virtual device 14 to first guest 10. First operating system12 may optionally restrict user space access to service functions.

In step S208, first application 16 requests the service functions fromhypervisor 30. Parameters from first application 16 may be passed as“call-by-value” parameters to second guest 20. First application 16announces a call back function to be called on completion of the servicefunction. First application 16 can announce regions of its memory areafor direct access by the service function. First application 16 invokesthe service of the service function asynchronously, i.e., system call 40is non-blocking, first application 16 continues to run, and firstapplication 16 is notified, i.e., called back on a previously registeredcall back function, when the service function completes. First operatingsystem 12 passes the service function request to hypervisor 30.

Then in step S210, hypervisor 30 informs second guest 20 of the requestfor the service functions by first application 16. Hypervisor 30provides virtual device 14. Virtual device 14 carries an identifier ofthe requested service function and call-by-value parameters, e.g., inconfiguration space. Virtual device 14 also provides base addressregisters that second guest 20 can use to access the memory of firstapplication 16 directly. Hypervisor 30 maps the announced memory offirst guest 10 on top of the memory of second guest 20. The base addressregister may contain an offset of the memory region in the address spaceof first application 16.

Next in step S212, second operating system 22 of second guest 20determines the request for service functions by hypervisor 30 on behalfof first application 16 has occurred by receiving the specialparavirtualized interrupt. Second operating system 22 may then searchfor available service function processes, i.e., blocking processes thatare ready to work on that service function. If none are found, but aservice of a service function is present, then the service function maybe queued for later processing. Second operating system 22 then mapsmemory regions as associated with the service function request into theaddress space of the process which will be working on the servicefunction. Second operating system 22 also announces the base address andsize of the memory of first guest 10 to the service function process ofsecond guest 20. Second operating system 22 provides service functionparameters to the AAC process, and schedules the service functionprocess, returning from its blocking system call 40.

In step S214, second application 26 services the request from firstapplication 16. Computation takes place until completion of the servicefunction request. The exported memory region of first application 16 ismapped by hypervisor 30 into a process address space of secondapplication 26. A base address register designates an offset of thememory region in the address space of first application 16. This may beused to follow pointers. Pointer dereferencing can either be doneimplicitly through compiler support, or explicitly through usingspecific code, e.g., via libraries. Upon completion, the servicefunction code returns potential return data (“by value”) in deviceregisters of virtual device 14. In addition, direct updates to thememory of first guest 10 may have taken place. The service functionprocess may inform second operating system 22 of renewed availability ofservice function processing capability, or terminate the service of theservice function for that identification.

Next in step S216, second operating system 22 of second guest 20notifies hypervisor 30 about the completion of the request. Secondoperating system 22 may withdraw access to the memory, e.g., removes thememory mapping, and may call hypervisor 30 to indicate completion of theservice function. If another service function request is pending, thenext service function request may be processed.

In step S218, hypervisor 30 indicates completion of the request to firstoperating system 12 of first guest 10. If hypervisor 30 realizes thatthe service function request is complete, then hypervisor 30 notifiesfirst operating system 12 and indicates the completion to first guest10, e.g., via interrupt on virtual device 14.

In step S220, first operating system 12 of first guest 10 informs firstapplication 16 of the completion of the request. First operating system12 calls a call-back function in the user space code of first guest 10to provide an indication of the completion of the service function bynotifying first application 16. The memory of first guest 10 has beenupdated directly during the process described in FIG. 2. Additionalcall-by-value return values are accessible through the virtual deviceregisters.

Referring now to FIG. 3, a schematic of an example of data processingsystem 310 is shown. Data processing system 310 is only one example of asuitable data processing system and is not intended to suggest anylimitation as to the scope of use or functionality of embodiments of theinvention described herein. Regardless, data processing system 310 iscapable of being implemented and/or performing any of the functionalityset forth herein above.

In data processing system 310 there is a computer system/server 312,which is operational with numerous other general purpose or specialpurpose computing system environments or configurations. Examples ofwell-known computing systems, environments, and/or configurations thatmay be suitable for use with computer system/server 312 include, but arenot limited to, personal computer systems, server computer systems, thinclients, thick clients, handheld or laptop devices, multiprocessorsystems, microprocessor-based systems, set top boxes, programmableconsumer electronics, network PCs, minicomputer systems, mainframecomputer systems, and distributed cloud computing environments thatinclude any of the above systems or devices, and the like.

Computer system/server 312 may be described in the general context ofcomputer system executable instructions, such as program modules, beingexecuted by a computer system. Generally, program modules may includeroutines, programs, objects, components, logic, data structures, and soon that perform particular tasks or implement particular abstract datatypes. Computer system/server 312 may be practiced in distributed cloudcomputing environments where tasks are performed by remote processingdevices that are linked through a communications network. In adistributed cloud computing environment, program modules may be locatedin both local and remote computer system storage media including memorystorage devices.

As shown in FIG. 3, computer system/server 312 in data processing system310 is shown in the form of a general-purpose computing device. Thecomponents of computer system/server 312 may include, but are notlimited to, one or more processors or processing unit(s) 316, a systemmemory 328, and a bus 318 that couples various system componentsincluding system memory 328 to processing unit(s) 316.

Bus 318 represents one or more of any of several types of busstructures, including a memory bus or memory controller, a peripheralbus, an accelerated graphics port, and a processor or local bus usingany of a variety of bus architectures. By way of example, and notlimitation, such architectures include Industry Standard Architecture(ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA)bus, Video Electronics Standards Association (VESA) local bus, andPeripheral Component Interconnect (PCI) bus.

Computer system/server 312 typically includes a variety of computersystem readable media. Such media may be any available media that isaccessible by computer system/server 312, and it includes both volatileand non-volatile media, removable and non-removable media.

System memory 328 can include computer system readable media in the formof volatile memory, such as random access memory (RAM) 330 and/or cachememory 332. Computer system/server 312 may further include otherremovable/non-removable, volatile/non-volatile computer system storagemedia. By way of example only, storage system 334 can be provided forreading from and writing to a non-removable, non-volatile magnetic media(not shown and typically called a “hard drive”). Although not shown, amagnetic disk drive for reading from and writing to a removable,non-volatile magnetic disk (e.g., a “floppy disk”), and an optical diskdrive for reading from or writing to a removable, non-volatile opticaldisk such as a CD-ROM, DVD-ROM or other optical media can be provided.In such instances, each can be connected to bus 318 by one or more datamedia interfaces. As will be further depicted and described below,system memory 328 may include at least one program product having a set(e.g., at least one) of program modules that are configured to carry outthe functions of embodiments of the invention.

Program/utility 340, having a set (at least one) of program modules 342,may be stored in system memory 328 by way of example, and notlimitation, as well as an operating system, one or more applicationprograms, other program modules, and program data. Each of the operatingsystem, one or more application programs, other program modules, andprogram data or some combination thereof, may include an implementationof a networking environment. Program modules 342 generally carry out thefunctions and/or methodologies of embodiments of the invention asdescribed herein.

Computer system/server 312 may also communicate with one or moreexternal devices 314 such as a keyboard, a pointing device, a display324, etc.; one or more devices that enable a user to interact withcomputer system/server 312; and/or any devices (e.g., network card,modem, etc.) that enable computer system/server 312 to communicate withone or more other computing devices. Such communication can occur viainput/output (I/O) interfaces 322. Still yet, computer system/server 312can communicate with one or more networks such as a local area network(LAN), a general wide area network (WAN), and/or a public network (e.g.,the Internet) via network adapter 320. As depicted, network adapter 320communicates with the other components of computer system/server 312 viabus 318. It should be understood that although not shown, other hardwareand/or software components could be used in conjunction with computersystem/server 312. Examples, include, but are not limited to: microcode,device drivers, redundant processing units, external disk drive arrays,RAID systems, tape drives, and data archival storage systems, etc.

The programs described herein are identified based upon the applicationfor which they are implemented in a specific embodiment of theinvention. However, it should be appreciated that any particular programnomenclature herein is used merely for convenience, and thus theinvention should not be limited to use solely in any specificapplication identified and/or implied by such nomenclature.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be any tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, a special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, a segment, or aportion of instructions, which comprises one or more executableinstructions for implementing the specified logical function(s). In somealternative implementations, the functions noted in the blocks may occurout of the order noted in the Figures. For example, two blocks shown insuccession may, in fact, be executed substantially concurrently, or theblocks may sometimes be executed in the reverse order, depending uponthe functionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The terminology used herein was chosen to best explain the principles ofthe embodiment, the practical application or technical improvement overtechnologies found in the marketplace, or to enable others of ordinaryskill in the art to understand the embodiments disclosed herein.

1.-17. (canceled)
 18. A computer program product for sharing memorybetween a first guest and a second guest both running on a dataprocessing system, the computer program product comprising: one or morecomputer readable storage device and program instructions stored on theone or more computer readable storage device, the program instructionsexecutable by a computer to cause the computer to perform a methodcomprising: program instructions to provide a virtual device to a firstguest for proxying memory accesses between the first guest and a secondguest, wherein the first guest is associated with the second guest by ahypervisor, and wherein the first guest is running a first operatingsystem and the second guest is running a second operating system; andprogram instructions to send one or more device related functions to thesecond guest, wherein the virtual device enables sharing memory betweenthe first guest and the second guest.
 19. The computer program productaccording to claim 18, wherein sharing memory between the first guestand the second guest, further comprises: program instructions toregister a second application running on the second guest with thesecond operating system in order to provide service functions; programinstructions to receive an announcement of availability of the servicefunctions to the hypervisor from the second operating system; programinstructions to receive an announcement of the service functions to thefirst guest from the hypervisor; program instructions to determine afirst application running on the first guest discovered the servicefunctions announced by the hypervisor; program instructions to determinethe first application requested the service functions from thehypervisor; program instructions to determine the hypervisor informedthe second guest of the request for the service functions by the firstapplication; program instructions to determine the second operatingsystem of the second guest received the request for service functions bythe first application; program instructions to service the request fromthe first application via the second application such that the requestis completed; program instructions to receive notification to thehypervisor of the completion of the request from the second operatingsystem of the second guest; program instructions to receive anindication of the completion of the request to the first operatingsystem of the first guest from the hypervisor; and program instructionsto receive notification to the first application of the completion ofthe request from the first operating system of the first guest.
 20. Acomputer system for sharing memory between a first guest and a secondguest both running on a data processing system, the computer systemcomprising: one or more computer processors; one or more computerreadable storage device; program instructions stored on the one or morecomputer readable storage device for execution by at least one of theone or more computer processors, the program instructions comprising:program instructions to provide a virtual device to a first guest forproxying memory accesses between the first guest and a second guest,wherein the first guest is associated with the second guest by ahypervisor, and wherein the first guest is running a first operatingsystem and the second guest is running a second operating system; andprogram instructions to send one or more device related functions to thesecond guest, wherein the virtual device enables sharing memory betweenthe first guest and the second guest.